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Thread: Odd interior heat/engine temp issue.

  1. #1

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    Odd interior heat/engine temp issue.

    A little quick background here. A few months back, I replaced the timing belt, water pump, thermostat, radiator hoses, and had the radiator completely boiled/cleaned at a radiator repair shop. This solved an overheating issue I was having at interstate speeds, and it also allowed me to fix a previous owner's botched timing belt replacement, in which he put the belt on one tooth off.

    Things have been great since then, with the temp gauge staying dead center in the middle. Until a week or so ago. These are the symptoms it is now exhibiting:


    • Engine starts and warms up as normal
    • Once at operating temperatures, it is fine when underway, temp gauge stays in the middle, and I have interior heat.
    • When I stop (stop light, traffic, etc) The temp gauge begins to climb, and at the same time, my interior heat begins to go cool. It will gradually go completely cold if I sit idling long enough.
    • The temp gauge, if I sit idling, will climb almost to the upper mark of the gauge, but not all the way to overheat.
    • Once I begin moving, the temp gauge drops, and my interior heat comes back.


    Coolant levels are normal and do not change.

    So, what do you guys think? Water pump was replaced with an Advance Auto reman, thermostat was stock temp replacement, pretty much the only thing I didn't replace or refurb was the heater core.

  2. #2

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    Your cooling fan is not working. Easy to replace if it's done for.
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  3. #3

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    Hmmm. Stock fan on a new fan clutch. How does a bad fan clutch explain the loss of interior heat?

  4. #4



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    when my subarus did that it meant the head gasket blew, but suby's are way worse than these trucks for that. Could have crud buildup in the core that idle coolant circulation can't overcome, although that won't explain the overheat - I agree with a bad fan clutch.
    Pennyman1
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  5. #5

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    Okay, I have new info to report. Start with the simplest things first, so I checked the coolant level in the radiator. Holy smokes, it's low. Add about a quart, maybe a little more. Hmm, what's this, the expansion tank is filled to the brim, it was not like that before, it was just filled to the "max" mark. Coolant in the expansion tank is not milky, like I think it would be with a head gasket, but I know that is not foolproof.

    So, i top up the coolant, let it idle in the driveway. Now temp gauge never gets above the first mark on the gauge, even after idling for 15 minutes. Upper hose is hot and tight feeling. Bottom rad hose is still cool.

    So, I'll throw this in there. Do I have a dud water pump? It is brand new, less that a 1000 miles on it. What that be causing these symptoms?

    Or, if it's a head gasket, what is the best way to know for sure?
    Last edited by leftfield6; 12-07-2014 at 07:50 PM.

  6. #6

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    Well, crud.

    Just took it for a 2 mile drive, got back, coolant expansion tank is brimming again, and the coolant in there looks creamy or actually looks like it's carbonated. I removed the cap and took a whiff Smells like exhaust fumes.

    I'll get one of the chemical head gasket test kits to be sure, but I'm thinking I've blown a head gasket.


  7. #7



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    sorry man - didn't want to be the bearer of bad news...
    Pennyman1
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  8. #8

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    My Subaru outback, sitting about 15 feet away from my truck, is chuckling at the irony.

  9. #9

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    I didn't consider a low coolant level when I suggested a fan clutch, but temperature gain at low speed is a common symptom of a bad fan clutch. Your full reservoir with low volume in the radiator would make me check the hose between the two, making sure it is allowing passage in either direction. I would also re torque head bolts before replacing head gasket. My $.02!
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  10. #10

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    Quote Originally Posted by lush90 View Post
    I didn't consider a low coolant level when I suggested a fan clutch, but temperature gain at low speed is a common symptom of a bad fan clutch. Your full reservoir with low volume in the radiator would make me check the hose between the two, making sure it is allowing passage in either direction. I would also re torque head bolts before replacing head gasket. My $.02!
    Hose is good between the expansion tank and the radiator. And there is absolutely exhaust smell in the coolant. But, I'll give retorqueing the head bolts a try. I don't think the heads been off before, but I have really no way of knowing.

    Maybe the same knucklehead who screwed up the timing belt did the head gasket!

  11. #11



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    Subys can be snarky like that - did it ever blow its gaskets?
    Pennyman1
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  12. #12

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    Quote Originally Posted by pennyman1 View Post
    Subys can be snarky like that - did it ever blow its gaskets?
    Nope. Non-turbo 2.5l in my 2006 Outback wagon with 156K on it. Head gaskets have never had a single issue. Her name is "Big Girl" and she is feeling a little bit superior right now, casting an eye over at the Ram50. I can practically hear the "harumph" snootiness.

  13. #13

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    Did you purge the air out of the cooling system after you changed the pump? I forgot once and I basically had the same problem, except for my hot air did not change from hot to cool, it just never got hot. And if air is trapped in the system, I would think it would raise the psi in the system above the psi rating on the radiator cap, which then the coolant flows into the res. If you end up draining the system I would check the thermostat to make sure it is opening properly if you can, or just get a new one. Hopefully you get things worked out!

  14. #14


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    you can check the head gasket with air pressure. you need a hose adapter to the spark plug hole (i use the hose from my compression checker)

    cycle the cylinder to TDC of the compression stroke, add compressed air (not too high or the engine will turn over and open the valves) look for bubbles in the radiator, air escaping sound from the oil cap is bad rings. you can also check for bad valves... air escaping sound in the intake, or exhaust.

    repeat for each cylinder.

  15. #15

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    No need for further diagnosis, IMHO. It's for sure the head gasket. i have a milky nasty latte in the radiator and expansion tank, plus I have exhaust gases in the radiator. I'm starting the tear-down a few weekends back, but haven't had a chance to get back to it. Hopefully I can make some progress on it later today.

  16. #16

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    Yeah i had the exact same thing with mine just the past two weeks, tore it apart and put back together. Mine also had compression going into coolant system so coolant was spewing out of overflow tank, and if i took off the radiator cap it would shoot 15 feet into the air. Quite the spectacle.

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